 (function(){
        change() 

        window.onresize = function(){
          change() 
        }

         window.orientationchange = function(){//orientationchange  屏幕旋转事件
          change() 
        }


        function change(){
          var winW = document.documentElement.clientWidth || document.body.clientWidth;
          document.documentElement.style.fontSize = winW *100 /750 +"px"
          console.log("1rem="+winW *100 /750 +"px")
        }
      })()